Credit

Caption

Coloured scanning electron micrograph (SEM) of Thallus surface of the orange crustose lichen (Xanthomendoza fallax). The marginal (ruffled) edges contain the vegetative reproductive bodies called soralia. The granules that break away from the soralia (and disperse) contain fragments of fungus and some algal cells. These powdery grains are called soredia. Lichens are a composite organism consisting of a fungus (mycobiont) and a photosynthetic alga (photobiont or phycobiont) growing together in a symbiotic relationship. The fungi and algae grow with their tissues entwined. The fungi receive sugars and other carbon compounds from the algae photosynthesis. The fungi produce lichen acids that are a mixture of special chemicals that are thought to protect both fungi and algae from being eaten by predators. Crustose lichens are slow growing and live to be very old. They colonize tree trunks, soil, and rock. Magnification: x41 when shortest axis printed at.